<template>
    <el-tooltip effect="dark"
                content="换肤"
                placement="bottom">
        <el-color-picker class="theme-picker"
                         popper-class="theme-picker-dropdown"
                         v-model="theme"
                         :size="size">
        </el-color-picker>
    </el-tooltip>
</template>

<script>
const version = require("element-ui/package.json").version; // element-ui version from node_modules
const ORIGINAL_THEME = "#409EFF"; // default color

export default {
    name: "ThemePicker",
    props: {
        default: {
            // 初始化主题，可由外部传入
            type: String,
            default: null
        },
        size: {
            // 初始化主题，可由外部传入
            type: String,
            default: "small"
        }
    },
    data () {
        return {
            chalk: "", // content of theme-chalk css
            theme: ORIGINAL_THEME,
            showSuccess: true // 是否弹出换肤成功消息
        };
    },
    mounted () {
        if (this.default != null) {
            this.theme = this.default;
            this.$emit("onThemeChange", this.theme);
            this.showSuccess = false;
        }
    },
    watch: {
        theme (val, oldVal) {
            if (typeof val !== "string") return;
            const themeCluster = this.getThemeCluster(val.replace("#", ""));
            const originalCluster = this.getThemeCluster(oldVal.replace("#", ""));
            console.log(themeCluster, originalCluster);
            const getHandler = (variable, id) => {
                return () => {
                    const originalCluster = this.getThemeCluster(
                        ORIGINAL_THEME.replace("#", "")
                    );
                    const newStyle = this.updateStyle(
                        this[variable],
                        originalCluster,
                        themeCluster
                    );

                    let styleTag = document.getElementById(id);
                    if (!styleTag) {
                        styleTag = document.createElement("style");
                        styleTag.setAttribute("id", id);
                        document.head.appendChild(styleTag);
                    }
                    styleTag.innerText = newStyle;
                };
            };

            const chalkHandler = getHandler("chalk", "chalk-style");

            if (!this.chalk) {
                const url = `https://unpkg.com/element-ui@${version}/lib/theme-chalk/index.css`;
                this.getCSSString(url, chalkHandler, "chalk");
            } else {
                chalkHandler();
            }

            const styles = [].slice
                .call(document.querySelectorAll("style"))
                .filter(style => {
                    const text = style.innerText;
                    return (
                        new RegExp(oldVal, "i").test(text) && !/Chalk Variables/.test(text)
                    );
                });
            styles.forEach(style => {
                const { innerText } = style;
                if (typeof innerText !== "string") return;
                style.innerText = this.updateStyle(
                    innerText,
                    originalCluster,
                    themeCluster
                );
            });

            // 响应外部操作
            this.$emit("onThemeChange", val);
            if (this.showSuccess) {
                this.$message({
                    message: "换肤成功",
                    type: "success"
                });
            } else {
                this.showSuccess = true;
            }
        }
    },
    methods: {
        updateStyle (style, oldCluster, newCluster) {
            let newStyle = style;
            oldCluster.forEach((color, index) => {
                newStyle = newStyle.replace(new RegExp(color, "ig"), newCluster[index]);
            });
            return newStyle;
        },

        getCSSString (url, callback, variable) {
            const xhr = new XMLHttpRequest();
            xhr.onreadystatechange = () => {
                if (xhr.readyState === 4 && xhr.status === 200) {
                    this[variable] = xhr.responseText.replace(/@font-face{[^}]+}/, "");
                    callback();
                }
            };
            xhr.open("GET", url);
            xhr.send();
        },

        getThemeCluster (theme) {
            const tintColor = (color, tint) => {
                let red = parseInt(color.slice(0, 2), 16);
                let green = parseInt(color.slice(2, 4), 16);
                let blue = parseInt(color.slice(4, 6), 16);

                if (tint === 0) {
                    // when primary color is in its rgb space
                    return [red, green, blue].join(",");
                } else {
                    red += Math.round(tint * (255 - red));
                    green += Math.round(tint * (255 - green));
                    blue += Math.round(tint * (255 - blue));

                    red = red.toString(16);
                    green = green.toString(16);
                    blue = blue.toString(16);

                    return `#${red}${green}${blue}`;
                }
            };

            const shadeColor = (color, shade) => {
                let red = parseInt(color.slice(0, 2), 16);
                let green = parseInt(color.slice(2, 4), 16);
                let blue = parseInt(color.slice(4, 6), 16);

                red = Math.round((1 - shade) * red);
                green = Math.round((1 - shade) * green);
                blue = Math.round((1 - shade) * blue);

                red = red.toString(16);
                green = green.toString(16);
                blue = blue.toString(16);

                return `#${red}${green}${blue}`;
            };

            const clusters = [theme];
            for (let i = 0; i <= 9; i++) {
                clusters.push(tintColor(theme, Number((i / 10).toFixed(2))));
            }
            clusters.push(shadeColor(theme, 0.1));
            return clusters;
        }
    }
};
</script>

<style>
.theme-picker .el-color-picker__trigger {
    vertical-align: middle;
}

.theme-picker-dropdown .el-color-dropdown__link-btn {
    display: none;
}
</style>
